There is no agreement regarding which solvent is more suitable to obtain sol–gel–derived titania (TiO2) samples with an enhanced photocatalytic behavior. Furthermore, the solvent effect on the preparation of TiO2-RGO (reduced graphene oxide) nanocomposites has not been published yet and could be an attractive experimental strategy to modulate structure and properties. On the basis of these observations, TiO2-RGO nanocomposites were fabricated in this study. It was evaluated for the influence of using either isopropyl (IsoprOH) or ethyl (EtOH) alcohol on the textural and photocatalytic properties of the prepared materials. The use of IsoprOH led to samples with smaller crystallite size, narrower apparent band gap, smaller isoelectric point, larger adsorption capacity, and higher photocatalytic activity. In addition, the incorporation of RGO into TiO2 greatly improved the adsorption capacity and photocatalytic activity of the latter. However, the optimal loading of RGO to prepare composites with enhanced photocatalytic activities was 1 wt%. This finding can be related to the stacking of RGO sheets when concentrations above 1 wt% are used, which could prevent UV light to reach the TiO2 particles and also decrease the photocatalytic capacity of the composites. Moreover, materials with RGO concentration above 1 wt% could exhibit a highly negatively charged surface, which may decrease the separation of the generated electron–hole pairs and lead to faster recombination rates of charge carriers.

Gold nanoparticles supported on titania catalysts with different Au loadings were prepared and evaluated in the reaction of NO reduction by CO in an oxygen rich condition. The crystalline structures of the Au/TiO2 materials were refined with Rietveld method. TiO2 support chiefly contains anatase phase, having a crystalline size ranged from 5 to 15 nm. Au particles have an average crystal size approximately 2-5 nm as Au concentration less 3 wt %. In the reaction of NO + CO + O2, the Au/TiO2catalysts show a selectivity to 100 % N2, neither NO2 nor N2O was yielded in the reaction temperature between 25 and 400 °C, which strongly indicates that Au/TiO2catalysts are much superior to the other catalysts like Pt/TiO2 catalysts on which N2O was usually produced in the reaction temperature below 200 °C and NO2 was produced in the reaction temperature above 300 °C under a similar reaction condition.

Titania nanotubes synthesized by a soft chemical process are described, having diameters of 8 nm to 10 nm and lengths ranging from approximately 0.1 μm to 1 μm. X-ray diffraction studies show the structure of the as-prepared nanotubes is the same as that of the starting anatase TiO2 nanoparticles. Energy-dispersive x-ray analysis and electron energy loss spectroscopy studies further indicate that the as-prepared nanotubes are composed of titania. Studies using transmission electron microscopy verified that the nanotubes are formed during alkali treatment, with subsequent acidic treatments having no effect on nanotube structure and shape.

We report on non-particulate titania photoelectrodes with a unique highly-ordered nanotube-array architecture prepared by an anodization process that enables precise control over array dimensions. Under 320–400 nm illumination titania nanotube-array photoanodes, pore size 110 nm, wall thickness 20 nm, and 6 μm length, generate hydrogen by water photoelectrolysis at a normalized rate of 80 mL/W•hr, to date the most efficient titania-based photoelectrochemical device, with a conversion efficiency of 12.25%. The highly-ordered nanotubular architecture allows for superior charge separation and charge transport, with a calculated quantum efficiency of nearly 100% for incident photons with energies larger than the titania bandgap.

In this study highly-ordered titania nanotube arrays of variable wall-thickness and length are used to photocleave water under ultraviolet irradiation. We demonstrate that the wall thickness, and length, of the nanotubes can be controlled via anodization bath composition and temperature. The nanotube length and wall thickness are key parameters influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For 22 nm inner-pore diameter nanotube-arrays 6 μm in length, with 9 nm wall thickness, upon 320–400 nm illumination at an intensity of 100 mW/cm2, hydrogen gas was generated at the power-time normalized rate of 51 mL/hr•W at an overall conversion efficiency of 12.5%. To the best of our knowledge, this hydrogen generation rate is the highest reported for a titania-based photoelectrochemical cell.

In this work, the high-temperature behavior of nanocrystalline TiO2 is studied using in situ transmission electron microscopy (TEM). These nanoparticles are made using wet chemical techniques that generate the anatase phase of TiO2 with average grain sizes of 6 nm. X-ray diffraction studies of nanophase TiO2 indicate the material undergoes a solid-solid phase transformation to the stable rutile phase between 600° and 900°C. This phase transition is not observed in the TEM samples, which remain anatase up to temperatures as high as 1000°C. Above 1000°C, nanoparticles become mobile on the amorphous carbon grid and by 1300°C, all anatase diffraction is lost and larger (50 nm) single crystals of a new phase are present. This new phase is identified as TiC both from high-resolution electron microscopy after heat treatment and electron diffraction collected during in situ heating experiments. Video images of the particle motion in situ show the nanoparticles diffusing and interacting with the underlying grid material as the reaction from TiO2 to TiC proceeds.